Transient mixed convection in a cavity. Comparison between water and sodium

The basic problem studied is the interaction between a vortex and a thermal stratification. The experiments are done in a parallelepipedic cavity which bottom communicates with a rectangular channel. A forced flow in this channel induces a recirculating flow in the cavity. The transient condition is a decrease (step wise or slope) of the inlet temperature at a constant flowrate. This problem is studied with two different approaches: experiments in water or in sodium. In the sodium experiments, the dimension of the cavity ensures large values of the Peclet number (about 104) and a wide range of values for the Richardson number (from 0.1 to 3). With these experiment, all the regimes of mixed convection, from forced convection to complete stratification can be covered. These results are compared with the other approach using a water model. This comparison is very helpful for studies on the thermalhydraulic behavior of Liquid Metal Fast Breeder Reactors. (author)